The overall hypothesis of the proposed research is that the neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) plays a regulatory role in the differential expression of the gonadotropin subunit genes that occurs during fetal and early postnatal sexual maturation. We propose that pituitary exposure to PACAP stimulates LHbeta and the common glycoprotein alpha-subunit but, delays the expression of FSHbeta during fetal development, and that a decrease in PACAP exposure results in the monotropic rise in FSH that occurs during the juvenile stage of sexual maturation in the male rat. The Specific Aims of the present proposal are: Aim 1. To determine whether PACAP plays a role in the differential expression of the gonadotropin subunit genes during fetal pituitary development. Aim 2. To determine if pituitary cells from fetal and infant rats are more responsive to PACAP than are cells from juvenile rats. Aim 3. To determine if the rose in FSHbeta mRNA in immature male rats is related to weaning, and is coincident with a change in PACAP expression in the hypothalamus or pituitary gland. Aim 4. To explore the developmental effects of PACAP through pituitary specific expression of the potent PACAP antagonist PACAP-(6-38).